The torque pulsation of an AC motor is preferably small from the viewpoint of vibration and noise. However, an inverter that supplies power to the AC motor realizes variable speed control, and thus is accompanied by a switching operation performed by a switching element (semiconductor element) (PWM control). Thereby, in a case where a harmonic voltage is generated and is applied to the AC motor, a harmonic current flows, which results in causing torque pulsation and vibration and noise.
In PTL 1, in switching control, the width of its OFF interval decreases monotonically from a fundamental voltage phase of 0 deg toward 90 deg, and is further optimized so that a harmonic current is minimized. Here, the fundamental voltage phase of 0 deg is a phase when the fundamental voltage (sine wave) of an inverter changes from negative to positive. In PTL 2, switching control is performed so as to lose half-wave symmetry in the interval of a width centering on a fundamental voltage phase of 180 deg±180 deg, and a harmonic current is reduced.